Retroviral agents have been implicated in a number of diseases, including cancer, autoimmune disease and AIDS. Human immunodeficiency virus (HIV) infection causes chronic progressive depletion of CD4.sup.+ T lymphocytes (CD4.sup.+ cells) and infection of macrophages, resulting in acquired immune deficiency syndrome. Currently zidovudine (AZT), an analogue of thymidine, is the primary anti-viral drug used in the treatment of HIV infection, although two other agents with a similar mechanism of action, dideoxyinosine (ddI) and dideoxycytosine (ddC), are also used. Colley, T. P. et al., New Engl. J. Med. (1990) 322:1340-45; Fischl, M. A., et al., New Engl. J. Med. (1987) 317:185-91. These agents are effective in inhibiting viral replication, and can stabilize the CD4.sup.+ cell levels, but they are unable to eliminate one of the major viral reservoirs, HIV infected macrophages. Gartner, S., et al., Science (1986) 233:215-19. Severe toxicity, particularly involving HIV host bone marrow is also associated with higher doses of AZT treatment, and the beneficial effects of the drug in AIDS patients diminishes after prolonged therapy; HIV strains resistant to AZT also have been observed in treated patients. These findings have prompted the search for alternative drugs for the treatment of HIV infection, particularly agents with a different mechanism of action.
Human immunodeficiency virus type 1 (HIV-1), a retrovirus, is the etiologic cause of AIDS. The HIV-1 envelope glycoprotein, gp120, specifically binds to the CD4 receptor on T lymphocytes and on monocytes and macrophages. Although infection of T lymphocytes requires cellular proliferation and DNA synthesis, productive infection of monocytes can occur independently of cellular DNA synthesis (Weinberg, J. B., et al,. (1991) J. Exp. Med. 174:1477-82). When HIV-1 infects activated CD4.sup.+ lymphocytes, it is lethal, but infected monocytes are relatively resistant to destruction by the virus. Consequently, these cells, once infected with HIV-1, serve as long-lived reservoirs of the virus. Not only are these cells a source of replicating virus, but their virally-mediated dysfunction may contribute to increased susceptibility to opportunistic infections that are the hallmark of AIDS.
Because monocyte-macrophages serve as reservoirs for HIV-1, selective targeting of this population, in addition to T lymphocytes, warrants further consideration (Finberg, R. W., et al., Science 252:1703-05, 1991. Early reports from Fox's group (JADA 118:709-711, 1989) indicated that a component of human saliva blocks HIV replication. More recently, Hattori (FEBS Lett. 248:48-52, 1989) showed that an inhibitor of tryptase (a trypsin-like enzyme) can inhibit syncytia formation of T-cells induced by HIV.
In exploring various potential modulators of HIV-1 infection, we have recently identified an endogenous source of inhibitory activity which retards HIV-1 infection and/or replication.
The factor responsible for the antiviral activity is serine leukocyte protease inhibitor (SLPI). SLPI is a potent inhibitor of human leukocyte elastase, chymotrypsin, cathepsin G, and of human trypsin, and has been purified from parotid secretions (Thompson, R. C. and K. Ohlsson, (1986) Proc. Natl. Acad. Sci. USA, 83:6692-96; and U.S. Pat. No. 4,760,130, both of which are incorporated herein by reference). SLPI is now available through production by recombinant DNA techniques; U.S. patent application No. 07/712,354, filed Jun. 7, 1991, PCT application No. W086/03519, filed Dec. 4, 1985, and European patent application 85 905 953.7, filed Dec. 4, 1985, each of which are incorporated herein by reference).
The ability of SLPI and/or its derivatives and analogs to block HIV-1 infection and/or replication can provide the basis for therapeutic intervention in HIV-1 infection.